Method for controlling combustion processes in an off-load internal combustion engine

ABSTRACT

The method is used for controlling incidences of combustion in an unloaded internal combustion engine ( 10 ) of a vehicle. In this connection, the following method steps are provided:  
     determining ( 12 ) a load-dynamics threshold;  
     detecting ( 12 ) an unloaded operating state of the internal combustion engine ( 10 );  
     detecting ( 12 ) an incidence of the load-dynamics threshold being exceeded in the unloaded operating state;  
     retarding ( 13 ) the ignition timing to form a load-dynamics aiming-off allowance that prevents combustion knock.  
     While the ignition timing is retarded ( 13 ), a unit ( 14 ) for adapting the knock-control dynamics is deactivated.

[0001] The present invention relates to a method for controllingincidences of combustion in an unloaded internal combustion engine of avehicle, in accordance with the introductory part of claim 1.

BACKGROUND INFORMATION

[0002] An unloaded operating state of an internal combustion engine canbe present, when, at the vehicle, no gear is engaged or the clutch isopened or the vehicle speed is equal to zero. In this context, it ispossible for very high load dynamics and engine-speed dynamics to setin, when the unloaded engine is revving at almost no load. Because ofthese increased load dynamics and engine-speed dynamics, the engine issubject to a higher tendency for combustion knock in the unloadedoperating state. However, this combustion knock during an unloadedoperating state of an internal combustion engine, which is also referredto as no-load revving, is particularly disadvantageous because effectiveand reliable knock control is made more difficult by the increaseddynamics (load dynamics and engine-speed dynamics) present. In addition,combustion knock especially has a disadvantageous effect on ride comfortduring an unloaded operating state, because it is easy to detectacoustically, and it is annoying in this operating state.

SUMMARY OF THE INVENTION

[0003] The method of the present invention for controlling incidences ofcombustion in an unloaded internal combustion engine of a vehicle ischaracterized by the following method steps:

[0004] determining a load-dynamics threshold;

[0005] detecting an unloaded operating state of the internal combustionengine;

[0006] detecting the exceeding of the load-dynamics threshold in theunloaded operating state;

[0007] retarding the ignition timing to form a load-dynamics aiming-offallowance.

[0008] By this means, the occurrence of a majority of combustion-knockincidences caused by the increased load dynamics and engine-speeddynamics setting in in the unloaded operating state may be prevented ina reliable and effective manner. Because of the increased tendency forcombustion knock, the load-dynamics aiming-off allowance to be set inthe unloaded operating state is greater than the load dynamics andengine-speed dynamics triggered in loaded operation, i.e. when the gearis engaged and the clutch is closed. By determining a load-dynamicsthreshold, it is possible to reliably and precisely define an operatingstate having increased knock tendency. Unloaded operation of theinternal combustion engine may be established as being when no gear isengaged or the clutch is opened (clutch pedal pressed down) or thevehicle speed is equal to zero. Therefore, it is possible to quickly andreliably detect a so-called “tip-in” operating state, according to whichthe engine undergoes no-load or nearly no-load revving in the unloadedoperating state, the probability of disadvantageous combustion knockoccurring increasing due to the increased load dynamics and engine-speeddynamics simultaneously setting in. After detecting this operatingsituation, which is critical with regard to the tendency for knock, itis advantageously possible to prevent combustion knock in the engine orat least limit it to as few combustion incidences as possible, byproducing a sufficient load-dynamics aiming-off allowance throughcorresponding retardation of the ignition timing.

[0009] The speed under load and the engine speed are advantageously usedas operating parameters for detecting an unloaded operating state of theengine and an engine-speed increase of the engine that is at leastnearly without load. In particular, the speed under load and enginespeed present themselves as operating parameters for detecting a“tip-in” operating state, according to which no-load or nearly no-loadrevving of the engine occurs, possibly along with the load-dynamicsthreshold being exceeded, when the clutch is disengaged or a gear is notengaged or the vehicle speed is equal to zero. In this context, thespeed under load and the engine speed may be ascertained in anespecially simple and precise manner.

[0010] According to a first embodiment variant, the ignition-timingretard value is calculated from an ignition-retard value dependent onthe engine speed. An ignition-retard value calculated as a function ofthe specific engine speed is particularly suitable for ensuring asufficient load-dynamics aiming-off allowance in a “tip-in” operatingstate.

[0011] According to a second, alternative embodiment variant, theignition-timing retard value is calculated from the sum of an adaptiveignition-retard value and an ignition-retard value dependent on theengine speed. In this manner, the necessary load-dynamics aiming-offallowance is calculated from an adaptive component and a componentdependent on the engine speed. In this connection, the value of theadaptive load-dynamics aiming-off allowance is known, while the value ofthe load-dynamics aiming-off allowance dependent on the engine speed isdetermined as a function of the specific engine speed present in theunloaded operating state.

[0012] While the ignition timing is retarded, the adaptation of theknock-control dynamics is advantageously deactivated. In particular,this allows the option of preventing the otherwise activated adaptationof the knock-control dynamics from unlearning the stored, adapted valuesascertained for loaded operating states, especially due to the adjusted,engine-speed-dependent load-dynamics aiming-off allowance. This allowsthe driveaway characteristics of the corresponding vehicle to bemarkedly improved after the unloaded operating state is brought to anend.

[0013] The ignition timing is advantageously retarded below apredeterminable vehicle-speed threshold. In doing this, dynamiccombustion knock, which is relatively easy for a vehicle user to hear ordetect, particularly at lower vehicle speeds, and therefore has anegative effect on the ride comfort, is prevented in the unloadedoperating state of the engine.

[0014] The present invention advantageously provides for theload-dynamics threshold being determined by a control device or storedin it, the unloaded operating state of the engine and the exceeding ofthe load-dynamics threshold in the unloaded operating state beingdetected by a detection unit, and the ignition timing being retarded byan ignition-timing adjustment unit to form a load-dynamics aiming-offallowance. This allows at least a reduction in the combustion knock in aquick and reliable manner, during a “tip-in” operating state of theinternal combustion engine.

[0015] Additional advantageous embodiments of the present invention arederived from the description.

BRIEF DESCRIPTION OF THE DRAWING

[0016] The FIGURE is explained below in detail in an exemplaryembodiment, using an appropriate drawing. In this context, the FIGUREshows a block diagram having a control device for controlling incidencesof combustion in an unloaded internal combustion engine.

DETAILED DESCRIPTION

[0017] The FIGURE shows a schematic representation of an internalcombustion engine 10 of a vehicle (not shown), which is operativelyconnected to a control device 11. Control device 11 has a detection unit12 for detecting a so-called “tip-in” operating state, anignition-timing adjustment unit 13, and a unit 14 for adapting theknock-control dynamics. A “tip-in” operating state is understood as anunloaded operating state of combustion engine 10, in which theprobability of disadvantageous combustion knock occurring increases dueto the setting-in of increased load dynamics and engine-speed dynamics.Combustion engine 10 is connected by a data-transmission linerepresented by arrow 15, to detection unit 12, which, for its part, isoperatively connected by control lines represented by arrows 19, 20, toignition-timing adjustment unit 13 and the unit 14 for adapting theknock-control dynamics. Ignition-timing adjustment unit 13 is connectedto the unit 14 for adapting the knock-control dynamics, using thecontrol line represented by double arrow 18. The two units 13, 14 arealso operatively connected to internal combustion engine 10 by controllines represented by arrows 16, 17.

[0018] Detection unit 12 is used to detect an unloaded operating stateof engine 10, as well as if a load-dynamics threshold is exceeded in theunloaded operating state. In this context, the engine speed of engine 10is used as an operating parameter. When a “tip-in” operating state hasbeen detected by detection unit 12, it transmits an appropriate signalto ignition-timing adjustment unit 13, via the control line representedby arrow 19. A deactivation signal is simultaneously transmitted bydetection unit 12, via the control line represented by arrow 20, to theunit 14 for adapting the knock-control dynamics, in order to block thelatter and thus intermittently shut it down during the detected “tip-in”operating state. Ignition-timing adjustment unit 13 calculates anengine-speed-dependent ignition-retard value, by which a load-dynamicsaiming-off allowance that prevents combustion knock may be obtained.This ignition-timing retard value is set at internal combustion engine10, using the control line represented by arrow 16. By this means, theload-dynamics aiming-off allowance generated by ignition-timingadjustment unit 13 prevents combustion knock in engine 10, or limits itto first, individual instances of combustion. The unit 14 for adaptingthe knock-control dynamics is deactivated during the detected “tip-in”operating state, so that no data or signals are transmitted by thecontrol lines represented by arrows 17, 18.

[0019] According to a second, alternative embodiment variant, theignition-timing retard value is calculated by ignition-timing adjustmentunit 13, from the sum of an adaptive ignition-retard value and anignition-retard value dependent on the engine speed. In this context,the adaptive ignition-retard value is transmitted by the unit 14 foradapting the knock-control dynamics, through the control linerepresented by double arrow 18, to ignition-timing adjustment unit 13.This adaptive ignition-retard value is an ignition-timing retard valuestored in the unit 14 for adapting the knock-control dynamics. In thiscase, this stored value is not changed or adapted during the “tip-in”operating state, since, according to this alternative embodimentvariant, the unit 14 for adapting the knock-control dynamics alsoremains deactivated during the “tip-in” operating state, so that adapteddata or signals are also not transmitted to engine 10 by the controlline 17 represented by an arrow.

[0020] The deactivation of knock-control-dynamics adaptation unit 14during the “tip-in” operating state is used to prevent the adaptedvalues stored in unit 14 from being unlearned. After the “tip-in”operating state is ended, the unit 14 for adapting the knock-controldynamics is restarted by detection unit 12, using the control line 20represented by arrow 20, in order to ensure effective and optimizedknock control in the subsequent load operation of engine 10. At the sametime, a corresponding, normal ignition-timing adjustment is carried outby ignition-timing adjustment unit 13.

[0021] Detection unit 12 is capable of monitoring additionaloperation-specific parameters, in order to initiate retardation of theignition timing in the unloaded operating state. An example of such anadditional operation-specific parameter is the vehicle speed, whichshould lie under a predeterminable vehicle-speed threshold, so that theretarding of the ignition timing in the unloaded operating state may belimited to a certain, lower vehicle-speed range, in which combustionknock particularly interferes with ride comfort.

[0022] A control device 11 that is formed and functions in this manneris advantageously capable of reliably and precisely preventingdisadvantageous combustion knock, or at least sharply limiting itsnumber of incidences.

[0023] The further structural and functional design of the specificunits of control device 11 is known per se and will therefore not bedescribed here in further detail.

What is claimed is:
 1. A method for controlling incidences of combustionin an unloaded internal combustion engine of a vehicle, characterized bythe following method steps: determining a load-dynamics threshold;detecting an unloaded operating state of the internal combustion engine;detecting the exceeding of the load-dynamics threshold in the unloadedoperating state; retarding the ignition timing to form a load-dynamicsaiming-off allowance.
 2. The method as recited in claim 1, wherein thespeed under load and the engine speed are used as operating parametersfor detecting an unloaded operating state of the engine and a speedincrease of the engine that is at least nearly without load.
 3. Themethod as recited in one of the preceding claims, wherein theignition-timing retard value is calculated from an ignition-retard valuedependent on the engine speed.
 4. The method as recited in one of thepreceding claims, wherein the ignition-timing retard value is calculatedfrom the sum of an adaptive ignition-retard value and an ignition-retardvalue dependent on the engine speed.
 5. The method as recited in one ofthe preceding claims, wherein the adaptation of the knock-controldynamics is deactivated while the ignition timing is retarded.
 6. Themethod as recited in one of the preceding claims, wherein the ignitiontiming is retarded below a predeterminable vehicle-speed threshold. 7.The method as recited in one of the preceding claims, wherein theload-dynamics threshold is determined by a control device (11) or storedin it, the unloaded operating state of the engine and the exceeding ofthe load-dynamics threshold in the unloaded operating state are detectedby a detection unit (12), and the ignition timing is retarded by anignition-timing adjustment unit (13), to form a load-dynamics aiming-offallowance.